System for and method of investigating the exact same point on a sample substrate with multiple wavelengths

ABSTRACT

Disclosed are system for and method of analyzing a sample at substantially the exact same small spot point on a sample with a plurality of wavelengths.

This Application is a CIP of Co-Pending Application Ser. No. 11/447,247Filed Jun. 5, 2006, and therevia of Ser. No. 10/426,590 Filed Apr. 30,2003, and therevia of Ser. No. 10/050,802 Filed Jan. 15, 2002 and Ser.No. 09/583,229 Filed May 30, 2000, and therevia Claims benefit ofProvisional Application Ser. No. 60/405,858 Filed Aug. 26, 2002.

TECHNICAL FIELD

The disclosed invention relates to the use of electromagnetic radiationto investigate sample systems, and more particularly to a method ofanalyzing the exact same small spot point on a sample system withmultiple wavelengths.

BACKGROUND

It is known to investigate sample systems with electromagnetic radiationby application of ellipsometers, polarimeters, reflectometers,spectrophotometers and the like. Prior art describes the use of lensesto focus a beam of electromagnetic radiation onto a sample and torecollimate it thereafter, and known Patent Applications describe use offocusing and/or collimating “Achromatic” Lenses before and/or after asample. Ideally an “Achromatic” lens provides the same focal length atall wavelengths in a beam of electromagnetism, however, practical“Achromatic” Lenses have focal lengths which vary with wavelength, in acyclic manner about an average. That is, a plot of Focal Length vs.Wavelength rises and falls such that a line drawn substantially parallelto the Wavelength Axis passes through said plot a plurality of times. Atsaid Focal Length then at least two, and typically more, wavelengths forwhich the Focal length is the same are identified. Achromatic Lenses canbe designed to set two desired wavelengths, (eg. 193 nm and 248 nm), andoften others will also result, on a determined, non-selected basis, atwhich the Focal Lengths are equal.

In ellipsometry it is often desirable to take data which pertains tomultiple wavelengths, and it is also important to investigate a samplewith said multiple wavelengths at exactly the same spot thereupon aswell as detect resulting data for each wavelength similarly. Thisrequires equal source and detector side focal lengths at saidwavelengths.

The disclosed invention then is a system of lenses which can be focusedon a sample at a plurality of wavelengths, and a method of their use inanalyzing a specific spot on a sample using electromagnetic radiationapplied at an oblique angle.

Another aspect of the disclosed invention is that a plurality of lenssets can be designed which provide different combinations of wavelengthsat which focal lengths are equal, and said plurality of sets of lensescan be mounted in, for instance an ellipsometer system, to allow them tobe sequentially positioned in the path of an electromagnetic beam, sothat more wavelengths can be sequentially caused to focus on the samespot on a sample.

A primary objective of the present invention is to provide a lens orlens system which is mounted so that it can be moved toward and awayfrom a sample, so as to sequentially cause different wavelengths tofocus on the same spot on a sample at different wavelengths. Where alens set provides equal focal lengths at each of a plurlaity ofwavelenghts, at a specific location thereof with respect to said sample,data can be simultaneously obtained for said plurlaity of wavelengths.

It is also noted that supplementing a minimal number of wavelengths withincreased number of angles-of-incidence can provide sufficient data setswhere necessary.

A search of Patents provided:

-   -   U.S. Pat. No. 7,057,757 which describes using lenses designed to        provide at least two wavelengths on a small spot on a sample,        which wavelengths have the same focal lengths    -   Patent to Ebstein, U.S. Pat. No. 5,091,801 which describes a        nearly index matched optic formed of at least two elements for        adjusting focal lengths;    -   a Patent to Noyes, U.S. Pat. No. 5,864,436 which describes an        objective lens which has the same focal length at two        wavelengths;    -   a Patent, U.S. Pat. No. 5,973,846 to McConica which describes an        auto focus system for a digital camera which has the focus of        two spectra offset from one another; and    -   a Patent, U.S. Pat. No. 5,078,513 to Spaulding et al., which        describes a lens in a waveguide of an integrated optical        waveguide which is corrected for chromatic dispersion.        Further:    -   a Patent to He et al., U.S. Pat. No. 5,963,327 is disclosed as        the Examiner identified it in Examination of Parent application        Ser. No. 10/426,590.    -   a Patent to Nakai al., U.S. Pat. No. 6,590,708 is disclosed as        the Examiner identified it in Examination of Parent application        Ser. No. 10/426,590.

Even in view of the prior art, a need remains for improved ellipsometer,polarimeter, reflectometer, spectrophotometer and the like systems whichinclude lenses that provide the same focal length at at least twowavelengths.

DISCLOSURE OF THE INVENTION

A disclosed invention method of analyzing a sample at the exact samespot with multiple wavelengths of electromagnetic radiation, comprisesthe steps of:

practicing steps a and b in either order, said steps a and b being:

-   -   a) providing a selection from the group consisting of:        -   ellipsometer;        -   polarimeter;        -   spectrophotometer; and        -   reflectometer;            which sequentially comprises a source of polychromatic            electromagnetic radiation, a stage for supporting a sample            and a detector;    -   b) providing a lens system which has been designed to allow        change of position thereof with respect to a sample, and        optionally provide focal lengths which are substantially exactly        the same at at least two specified wavelengths;    -   c) placing one of said lenses provided in step b prior to a        sample which is positioned on said stage for supporting a        sample, and one of said after said sample;    -   d. causing polychromatic electromagnetic radiation from said        source thereof to become focused onto said sample by said        pre-sample lens, and obtaining data at wavelengths at which        focal lengths are equal such that they are focused onto said        sample at substantially exactly the same point thereupon;    -   e. moving the lens systems along the locus of the        electromagnetic radiation, to be at a different distance from        said sample and again causing polychromatic electromagnetic        radiation from said source thereof to become focused onto said        sample by said pre-sample lens, and obtaining data at at least        one wavelength at which the focal length is such as to be        focused onto said sample at substantially exactly the same point        thereupon as in step d;    -   f) utilizing only data obtained which correspond to said        substantially same point on said sample in sample analysis.

Said method of analyzing a sample at the exact same spot can includesteps a-d being repeated using a second lens system which is designed toprovide the same substantially equal focal length at at least twowavelengths, at least one of said at least two wavelengths beingdifferent from the two wavelengths provided by the lens systems providedin step b, and wherein step e additionally utilizes data obtained atsaid additional at least two wavelengths in said sample analysis.

A modified recital of the method of analyzing a sample at the exact samespot with at least two wavelengths of electromagnetic radiation,comprising the steps of:

practicing steps a and b in either order, said steps a and b being:

-   -   a) providing a selection from the group consisting of:        -   ellipsometer;        -   polarimeter;        -   spectrophotometer; and        -   reflectometer;            which sequentially comprises a source of polychromatic            electromagnetic radiation, a stage for supporting a sample            and a detector;    -   b) providing:    -    b1) a first set of two lenses which have been designed to        provide focal, lengths which are substantially exactly the same        at two specified wavelengths; and    -    b2) a second set of two lenses which have been designed to        provide focal lengths which are substantially exactly the same        at two specified wavelengths, at least one of said wavelengths        being different than the two wavelengths in the first set of        lenses provided in step b1;    -   c) placing one of said lenses provided in step b1 prior to a        sample which is positioned on said stage for supporting a        sample, and one of said lenses provided in step b1 after said        sample, each of said lenses being placed a focal length distance        from a specific point on said sample;    -   d. causing polychromatic electromagnetic radiation from said        source thereof to become focused onto said sample by said        pre-sample lens, such that said two wavelengths are focused onto        said sample at substantially exactly the same point thereupon,        such that via reflection from said sample said two wavelengths        are entered into said detector;    -   e) placing one of said lenses provided in step b2 prior to a        sample which is positioned on said stage for supporting a        sample, and one of said lenses provided in step b1 after said        sample, each of said lenses being placed a focal length distance        from a specific point on said sample;    -   f) causing polychromatic electromagnetic radiation from said        source thereof to become focused onto said sample by said        pre-sample lens, such that said two wavelengths are focused onto        said sample at substantially exactly the same point thereupon,        such that via reflection from said sample said two wavelengths        are entered into said detector;    -   g) analyzing said sample utilizing only data provided by said        detector based upon said wavelengths for which the focal lengths        of the lenses provided in steps b1 and b2 are substantially the        same.

It is also within the scope of the disclosed invention to allow thefocal lengths at said two wavelengths to vary a bit, within anacceptable range. In that case the method of analyzing a sample at theexact same spot with at least two wavelengths of electromagneticradiation, comprises the steps of:

practicing steps a and b in either order, said steps a and b being:

-   -   a) providing a selection from the group consisting of:        -   ellipsometer;        -   polarimeter;        -   spectrophotometer; and        -   reflectometer;            which sequentially comprises a source of polychromatic            electromagnetic radiation, a stage for supporting a sample            and a detector;    -   b) providing two lens systems which have been designed to        provide ranges of wavelengths in Focal Length vs. Wavelength        plots, for which wavelengths in said ranges of wavelengths the        focal lengths are centered about two intended specified        wavelengths, variance in said focal lengths being within an        acceptable range;    -   c) placing one of said lens systems provided in step b prior to        a sample which is positioned on said stage for supporting a        sample, and one of said lens systems after said sample, each of        said lens systems being placed a focal length distance from a        specific point on said sample;    -   d. causing ploychromatic electromagnetic radiation from said        source thereof to become focused onto said sample by said        pre-sample lens system, such that said ranges of wavelengths        around said two wavelengths are focused onto said sample at        substantially exactly the same point thereupon.    -   e) utilizing only data obtained at said wavelengths for which        the focal lengths are within acceptable ranges of deviation from        being substantially the same, in sample analysis.

Again, said method can involve analyzing the sample at the exact samespot in which steps a-d are repeated using additional lens systems whichare designed to provide substantially the same equal focal lengths at atleast two additional wavelengths, using lenses which are designed toprovide ranges of substantially equal focal lengths around at least twoadditional wavelengths, at least one of said two additional wavelengthsbeing different from the two wavelengths provided by the lenses providedin the first practice of step b.

A modified method of analyzing a sample at the exact same spot with atleast two wavelengths of electromagnetic radiation, comprising the stepsof: practicing steps a and b in either order, said steps a and b being:

-   -   a) providing a selection from the group consisting of:        -   ellipsometer;        -   polarimeter;        -   spectrophotometer;        -   reflectometer; and        -   functional equivalent;            which sequentially comprises a source of polychromatic            electromagnetic radiation, a stage for supporting a sample            and a detector;    -   b) providing a set of two lenses which have been designed to        provide a first focal length which is substantially exactly the        same at first and second specified wavelengths, and a second        focal length which is substantially exactly the same at third        and forth specified wavelengths; and    -   c) placing one of said lenses provided in step b prior to a        sample which is positioned on said stage for supporting a        sample, and one of said lenses provided in step b after said        sample, each of said lenses being placed a focal length distance        from a specific point on said sample;    -   d) causing polychromatic electromagnetic radiation from said        source thereof to become focused onto said sample by said        pre-sample lens, such that said first and second wavelengths are        focused onto said sample at substantially exactly the same point        thereupon, such that via reflection from said sample said two        wavelengths are entered into said detector;    -   e) causing said lenses to be moved along the locus of the        electromagnetic radiation toward or away from said sample, such        that the said third and forth wavelengths are focused onto said        sample at substantially exactly the same point thereupon as was        investigated in step d, such that via reflection from said        sample said two wavelengths are entered into said detector;    -   f) causing polychromatic electromagnetic radiation from said        source thereof to become focused onto said sample by said        pre-sample lens, such that said two wavelengths are focused onto        said sample at substantially exactly the same point thereupon,        such that via reflection from said sample said two wavelengths        are entered into said detector;    -   g) analyzing said sample utilizing only data provided by said        detector based upon said first, second, third and forth        wavelengths.

A disclosed invention system can be described as being selected from thegroup consisting of:

-   -   ellipsometer;    -   polarimeter;    -   spectrophotometer;    -   reflectometer;    -   and functionally similar systems;        which sequentially comprises a source of polychromatic        electromagnetic radiation, a stage for supporting a sample and a        detector. Said system being characterized by lens systems which        have been designed to provide focal lengths which are        substantially exactly the same at two specified wavelengths, one        of said lens systems being placed prior to a sample which is        positioned on said stage for supporting a sample, and one of        said lens systems after said sample, each of said lens systems        being placed a focal length distance from a specific point on        said sample.

As a specific example, the disclosed invention can also be considered tobe an ellipsometer system sequentially comprising elements selected fromthe group consisting of:

-   -   a. a Source of a polychromatic beam electromagnetic radiation;    -   b. a Polarizer element;    -   c. optionally a compensator element;    -   d. focusing means;    -   e. a material system;    -   f. collimating means;    -   g. optionally a compensator element;    -   h. an Analyzer element; and    -   i. a Detector System;        in which said focusing means in d and collimating means in f        comprise input and output lenses mounted to allow change of        position thereof with respect to a sample, and optionally        provide focal lengths which are substantially exactly the same        at at least two specified wavelengths;        such that in use polychromatic electromagnetic radiation from        said source thereof is caused to become focused onto said sample        and data is obtained at wavelengths at which focal lengths are        equal such that they are focused onto said sample at        substantially exactly the same point thereupon;        followed by moving the lenses to be at a different distances        from said sample, along the locus of the electromagnetic        radiation, and again causing said polychromatic electromagnetic        radiation from said source thereof to become focused onto said        sample by said pre-sample lens, and obtaining data at at least        one wavelength at which the focal length is such that the        polychromatic electromagnetic radiation is focused onto said        sample at substantially exactly the same point thereupon as in        step d; and        utilizing only data obtained which correspond to said        substantially same point on said sample in sample analysis.

The disclosed invention can be characterized as a lens system withapplication in ellipsometer and polarimeter systems whereinbirefringence, and spectroscopic electromagnetic beam spot sizechromatic dispersion reduction and focal length chromatic dispersionreduction is desired, said lens system comprising at least twosequentially oriented elements, one of said two sequentially orientedelements being of a shape and, orientation which individually convergesa beam of electromagnetic radiation caused to pass therethrough, and theother being of a shape and orientation which individually diverges abeam of electromagnetic radiation caused to pass therethrough, whereinsaid convergence effect is greater than said divergence effect; therebeing a region between said at least two elements such that, in use, abeam of electromagnetic radiation sequentially passes through one ofsaid at least two elements, then said region therebetween, and then theother of said at least two elements before emerging as an effectivelyconverged, focused, beam of electromagnetic radiation; said lens systembeing characterized in that the focal lengths at two or threewavelengths are exactly the same.

The disclosed invention can be described as a dual stage lens systemwith application in ellipsometer systems, said dual stage lens systemcomprising two sequentially oriented lens systems, each of said twosequentially oriented lens systems being comprised of:

-   -   at least two sequentially oriented lens elements, one of said at        least two sequentially oriented lens elements being of a shape        and orientation which individually converges a beam of        electromagnetic radiation caused to pass therethrough, and the        other being of a shape and orientation which individually        diverges a beam of electromagnetic radiation caused to pass        therethrough, there being a region between said at least two        lens elements such that, in use, a beam of electromagnetic        radiation sequentially passes through one of said at least two        lens elements, then said region therebetween, and then the other        of said at least two lens elements before emerging as a focused        beam of electromagnetic radiation; said dual stage lens system        comprising at least two sequentially oriented lens elements        being a selection from the group consisting of:        -   a sequential combination of a converging element, a            diverging element, a converging element and a diverging            element;        -   a sequential combination of a converging element, a            diverging element, a diverging element and a converging            element;        -   a sequential combination of a diverging element, a            converging element, a diverging element and a converging            element;        -   a sequential combination of a diverging element, a            converging element, a converging element and a diverging            element.            said two sequentially oriented lens systems each having            exactly the same focal length at two wavelengths.

In general the lense systems typically presents with said a convergingelement selected from the group consisting of:

-   -   a bi-convex;    -   a plano-convex with an essentially flat side;        and presents with said diverging element selected from the group        consisting of:    -   a bi-concave lens element;    -   a plano-concave with an essentially flat side.

Further, said lens systems typically comprise a selection from the groupconsisting of:

-   -   a) a sequential combination of a bi-convex element and a        bi-concave element;    -   b) a sequential combination of a bi-concave element and a        bi-convex element;    -   c) a sequential combination of a bi-convex element and a        plano-concave element with said concave side of said        plano-concave element adjacent to said bi-convex element;    -   d) a sequential combination of a bi-convex element and a        plano-concave element with said essentially flat side of said        plano-concave element being adjacent to said bi-convex element;    -   e) a sequential combination of a plano-concave element and a        bi-convex element with said essentially flat side of said        plano-concave element adjacent to said bi-concave element;    -   f) a sequential combination of a plano-concave element and        bi-convex element with said concave side of said plano-concave        element adjacent to said bi-convex element;    -   g) a sequential combination of a plano-convex element and a        bi-concave element with said essentially flat side of said        plano-convex element adjacent to said bi-concave element;    -   h) a sequential combination of a bi-concave element with a        plano-convex element with said convex side of said plano-convex        element adjacent to said bi-concave element;    -   i) a sequential combination of a plano-concave element and a        plano-convex element with the essentially flat side of said        plano-concave element being adjacent to the convex side of the        plano-convex element;    -   j) a sequential combination of a plano-concave element and a        plano-convex element with the essentially flat side of said        planoconcave element being adjacent to the convex side of said        plano-convex element;    -   k) a sequential combination of a plano-convex element and a        plano-concave element with the essentially flat side of said        plano-covex element and the essentially flat side of said        plano-concave element being adjacent to one another;    -   l) a sequential combination of a plano-concave element and a        plano-convex element with the concave side of said plano-concave        element being adjacent to the convex side of the plano-convex        element;    -   m) a sequential combination of a plano-convex element and a        bi-concave element with said convex side of said plano-convex        element adjacent to said bi-concave element;    -   n) a sequential combination of a bi-concave element and a        plano-convex element with said essentially flat side of said        plano-convex element adjacent to said bi-concave element;    -   o) a sequential combination of a plano-convex element and a        plano-concave element with said convex side of said plano-convex        element adjacent to the concave side of the plano-concave        element;    -   q) a sequential combination of a plano-concave element and a        plano-convex element with said essentially flat side of said        plano-convex element being adjacent to the essentially flat side        of the plano-concave element;    -   r) a sequential combination of a plano-convex element and a        plano-concave element with said convex side of said plano-convex        element being adjacent to the essentially flat side of the        plano-concave element;    -   s) a sequential combination of a plano-concave element with a        plano-convex-element with the essentially flat side of said        plano-convex element being adjacent to the concave side of said        plano-concave element;        and wherein said region between said at least two elements has        essentially the optical properties of a selection from the group        consisting of:    -   a void region; and    -   a functional equivalent to a    -   void region.

And further yet, each of said at least two elements is typically made ofa material independently selected from the group consisting of:

-   -   CaF₂;    -   BaF₂;    -   LiF;    -   MgF₂; and    -   fused silica;        and wherein each of said at least two elements are individually        selected to be made of different materials. One embodiment, for        instance, provides lens systems wherein one of said at least two        lens elements in each of said two sequentially oriented lenses        is made of CaF₂ and the other element in each of said two        sequentially oriented lenses is made of fused silica.

It is also noted that the focal length of said lens systems is oftenselected to be between forty and forty-one millimeters, based onpractical ellipsometer system dimensions.

Another embodiment of the present invention sample analysis systemcomprises

-   -   a) a source of beam of polychromatic electromagnetic radiation;    -   b) a scanning monochromater;    -   c) a system comprising a lens and means for adjusting the        position thereof in a direction along the locus of said beam;    -   d) a sample;    -   e) a system comprising a lens and means for adjusting the        position thereof in a direction along the locus of said beam of        polychromatic electromagnetic radiation after it reflects from        said sample; and    -   f) a detector.        Said system further comprises a computer control system which is        programmed to provide signals to the scanning monochromater, the        system comprising a lens and means for adjusting the position        thereof in a direction along the locus of said beam in c, and        said a system comprising a lens and means for adjusting the        position thereof in a direction along the locus of said beam of        polychromatic electromagnetic radiation after it reflects from        said sample in e. In use, as the scanning monochromater provides        a sequence of wavelengths, the the system comprising a lens and        means for adjusting the position thereof in a direction along        the locus of said beam in c, and said a system comprising a lens        and means for adjusting the position thereof in a direction        along the locus of said beam of polychromatic electromagnetic        radiation after it reflects from said sample in e are caused to        move such that their focal lengths at each wavelength provided        by said scanning monochromater provides the same substantially        focused small spot is encountered on said sample. Said system        can further comprise a polarizer between said source of beam of        polychromatic electromagnetic radiation and said sample, and an        analyzer between said sample and said detector, and the system        analysis system is an ellipsometer or polarimeter system. Said        system can further comprise at least one compensator situated in        the path of said beam of polychromatic electromagnetic radiation        between said source of beam of polychromatic electromagnetic        radiation and the detector thereof.

It is noted that Methodology of the present invention can involvepresenting the results of practicing said methodology, expressly oreffectively.

Finally, it is noted that purging or evacuation, to reduce the presenceof oxygen and/or water vapor etc. which absorb energy from certainwavelengths, can be practiced in conjunction along with the recitedmethodology steps to improve achieved results.

The invention will be better understood by reference to the DetailedDescription Section of theis Disclosure, in combination with theDrawings.

SUMMARY

It is therefore a purpose and/or objective of the disclosed invention toteach a system for and method of analyzing., via use of electromagneticradiation, substantially the exact same point on a sample system with atleast two wavelengths mediated by varying the location of focusingmeans.

It is another purpose and/or objective of the disclosed invention todisclose optional use of multi-element lenses which are ground toprovide the exact same focal length at two selected wavelengths.

It is a further purpose of and/or objective of the disclosed inventionto disclose coordinated operation of a scanning monochromater and a lensfocusing system to sequentially provide a series of wavelengths to asample, each of which is focused onto substantially the exact same smallspot.

Other purposes and/or objectives will become apparent by a reading ofthe Specification and Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a demonstrates an ellipsometer system with both reflection andtransmission pathways indicated.

FIG. 1 b shows an alternative reflection mode ellipsometer system.

FIG. 1 c shows a top view of the FIG. 1 b ellipsometer system.

FIG. 1 d shows a system comprising a coordinated scanning monochromatorand a lens focusing system.

FIGS. 1 e 1 and 1 e 2 demonstrate single and multiple stagemulti-element lens systems which provide quasi-achromatic focal lengthsand spot sizes.

FIGS. 1 f-1 w show various multi-element lens confugurations which canprovide quais-achromatic focal length vs. wavelength.

FIGS. 1 x-1 zz show sequences in multi-lens configurations.

FIGS. 2 a and 2 b show focal length vs. wavelengths for various lenstypes, including quasi-achromatic lenses.

FIG. 2 c shows spot size vs. wavelength for various lenses, including aquasi-achromatic lens.

FIG. 3 a 1 demonstrates a basic ellipsometers sytems comprising lensesF1 and F2 in input and output sides of a sample system. Said F1 and F2can be in a slidable S1, S2 or S3 as shown in FIGS. 3 b abd 3 c, whichslides into and out of the paper.

FIG. 3 a 2 indicates that a system can be constructed to allow moving asingle lens toward or away from a sample.

FIG. 3 a 3 shows another approach to providing a sequence of lenses (F1)(F1′) (F1″) and (F2) (F2′) and (F2″) into the beam (E) ofelectromagnetic radiation.

FIGS. 3 b and 3 c demonstrate slidable multiple input/output lenscombinations.

FIGS. 4 a and 4 b demonstrate purging systems.

FIG. 5 demonstrates the sort of express display of results that can begenerated by application of the present invention.

DETAILED DESCRIPTION

Turning now to the Drawings, FIG. 1 a demonstrates an ellipsometer orpolarimeter system with both reflection and transmission pathwaysindicated. Note there is s Polarization State Generator (PSG) whichcomprises a Source of Electromagnetic Radiation (LS), a Polarizer (P), aCompensator (C1), Additional Element (AC1) which for the purposes ofthis disclosure can be considered to be a focusing lens, such asidentified as (F1) in FIG. 1 b. Also shown are Reflection andTransmission Mode Polarization State Detector Systems (PSD). (PSD′)which each comprise Additional Elements (AC2) (AC2′), Compensator (C2)(C2′), Analyzer (A) (A′), and Detector (DET) (DET′). Note the theAdditiona Component (AC2) can be considered a Focusing Lens, such as(F2) in FIG. 1 b. In use the Source of Electromagnetic Radiation (LS)provides a (polychromatic) beam of electromagnetic radiation which isprovided a polarizations atate by Polarizer (P) and Compensator (C1),then is focused into Sample (SS) by Additional Element (AC1). Afterinteraction with the Sample System (SS) the beam enters PolarizationState Detector (PSD) (PSD′). It is note that the Compensators (C1) (C2)(C2′) can be eliminated.

FIG. 1 b shows a Reflection Mode variation on the System shown in FIG. 1a. Shown are a Source of Electromagnetic Radiation (LS), a Polarizer(P), a First Reflective Means (PRI), a Focusing Lens (F1), a SampleSystem (SS) on a Stage (STG), a Colimating Lens (F2) a Second ReflectiveMeans (PRO), an Analyzer (A) and a Detector (DET) which provides entrythereinto via an Aperture (A). FIG. 1 c shows a top view of the Systemof FIG. 1 b. It is noted that (PRI) and (PRO) can be made of the samematerial, but the preferred embodiment provides that (PRI) be made ofBK7 (refractive index approximately 1.55) and that (PRO) be made of F2(refractive index approximately 1.7).

FIG. 1 d shows a system comprising a coordinated Scanning Monochromator(SM) and a Lens Focusing Control System (LFCS), comprised of Source (LS)side (LSI) and Detector side (LSO) components. In use the ComputerControl System (CC) causes Scanning Monochromator to scan through asequence of wavelengths and them one at a time toward the Sample (S),and simultaneously controls the Lens Focus Control System (LFCS) suchthat essentially perfect focus is achieved on the Sample (S) Surface ateach wavelength. This approach can be very beneficial where as small aspossible sample spot size is desired to be investigated. It is notedthat magnetostriction systesm are available which allow nanometermovement of lenses. Thus it is possible to set very precise focallengths corresponding to each wavelength. Further, while the system ofFIG. 3 a 2 is preferably applied in the FIG. 1 d invention embodiment,said embodiment should be considered sufficiently broad to include FIG.3 a 1 or FIGS. 3 a 3, 3 b and 3 c systems, (see disclosure later in thisSection).

FIG. 1 e 1 shows a Lens comprised of multiple elements (FE_(1a)),(FE_(2a)) and (FE_(3a)). FIG. 1 e 2 shows a sequential two Lens Systemin which the First Lens comprises (FE_(3a)) (FE_(2a)) and (FE_(1a)) andin which the Second Lens comprises (FE_(1b)), (FE_(2b)) and (FE_(3b)).The purpose of multi-element lenses is to provide more achromaticcharacteristics than is possible with single element lenses.

FIGS. 1 f-1 w are included to provide insight to various FIG. 1 e 1Single Multi-Element Lens configurations, and FIGS. 1 x-1 zz areincluded to show that FIG. 1 e 2 two lense systems can be constructed ofalternating Converging (C), (eg. the First Lens Element in FIG. 1 f),and Diverging (D), (eg. the Second Element in FIG. 1 f), lenses in anyfunctional order. It is not the purpose of this Disclosure to describeany specific Lens constuction, but rather to provide insight as togeneral Multiple Element Lens constructions, the Elements of which canbe ground to provide exactly the same Focal Length at two selectedwavelengths. A present invention lens system, which is particulary wellsuited for application in ellipsometer systems, then provides forspectroscopic electromagnetic beam spot size and focal length chromaticdispersion reduction by configuring at least two sequentially orientedelements, one of said at least two sequentially oriented elements beingof a shape and orientation which individually converges a beam ofelectromagnetic radiation caused to pass therethrough, and the otherbeing of a shape and orientation which individually diverges a beam ofelectromagnetic radiation caused to pass therethrough, there being aregion between said first and second elements such that, in use, a beamof electromagnetic radiation sequentially passes through said firstelement, then said region therebetween, and then said second elementbefore emerging as a focused beam of electromagnetic radiation. Such alens system with application in ellipsometer systems is characterized bya converging element which presents as a selection from the groupconsisting of:

-   -   a bi-convex;    -   a plano-convex with an essentially flat side;        and said diverging element is characterized as a selection from        the group consisting of:    -   a bi-concave lens element;    -   a plano-concave with an essentially flat side.        Further, as shown in FIGS. 1 f-1 w, said present invention lens        systems can comprise a selection from the group consisting of:    -   a) a sequential combination of a bi-convex element and a        bi-concave element;    -   b) a sequential combination of a bi-concave element and a        bi-convex element;    -   c) a sequential combination of a bi-convex element and a        plano-concave element with said concave side of said        plano-concave element adjacent to said bi-convex element;    -   d) a sequential combination of a bi-convex element and a        plano-concave element with said essentially flat side of said        plano-concave element being adjacent to said bi-convex element;    -   e) a sequential combination of a plano-concave element and a        bi-convex element with said essentially flat side of said        plano-concave element adjacent to said bi-concave element;    -   f) a sequential combination of a plano-concave element and        bi-convex element with said concave side of said plano-concave        element adjacent to said bi-convex element;    -   g) a sequential combination of a plano-convex element and a        bi-concave element with said essentially flat side of said        plano-convex element adjacent to said bi-concave element;    -   h) a sequential combination of a bi-concave element with a        plano-convex element with said convex side of said plano-convex        element adjacent to said bi-concave element;    -   i) a sequential combination of a plano-concave element and a        plano-convex element with the essentially flat side of said        plano-concave element being adjacent to the convex side of the        plano-convex element;    -   j) a sequential combination of a plano-concave element and a        plano-convex element with the essentially flat side of said        planoconcave element being adjacent to the convex side of said        plano-convex element;    -   k) a sequential combination of a plano-convex element and a        plano-concave element with the essentially flat side of said        plano-covex element and the essentially flat side of said        plano-concave element being adjacent to one another;    -   l) a sequential combination of a plano-concave element and a        plano-convex element with the concave side of said plano-concave        element being adjacent to the convex side of the plano-convex        element;    -   m) a sequential combination of a plano-convex element and a        bi-concave element with said convex side of said plano-convex        element adjacent to said bi-concave element;    -   n) a sequential combination of a bi-concave element and a        plano-convex element with said essentially flat side of said        plano-convex element adjacent to said bi-concave element;    -   o) a sequential combination of a plano-convex element and a        plano-concave element with said convex side of said plano-convex        element adjacent to the concave side of the plano-concave        element;    -   q) a sequential combination of a plano-concave element and a        plano-convex element with said essentially flat side of said        plano-convex element being adjacent to the essentially flat side        of the plano-concave element;    -   r) a sequential combination of a plano-convex element and a        plano-concave element with said convex side of said plano-convex        element being adjacent to the essentially flat side of the        plano-concave element;    -   s) a sequential combination of a plano-concave element with a        plano-convex element with the essentially flat side of said        plano-convex element being adjacent to the concave side of said        plano-concave element;        and wherein said region between said first and second elements        having essentially the optical properties of a selection from        the group consisting of:    -   a void region; and    -   a functional equivalent to a    -   void region.

A present invention lens system with application in ellipsometer systemscan be further characterized in that the converging element of saidfirst and second elements is typically made of a material independentlyselected from the group consisting of:

-   -   CaF₂;    -   BaF₂;    -   LiF; and    -   MgF₂;        and the diverging element of said first and second elements is        selected to be made of fused silica, although it is within the        scope of the present invention to make the converging element of        fused silica and the diverging element of a selection from the        group consisting of CaF₂; BaF₂; LiF; and MgF₂. It is noted that        lens elements made of MgF₂ are typically bi-refringent whereas        lens elements made of CaF₂; BaF₂ and LiF typically demonstrate        far less bi-refringence, unless subjected to stress.

A present invention lens system with a focal length of fifty millimetersor less, with application in ellipsometer systems, can be described asbeing comprised of lens system comprising two sequentially orientedlenses, each of said sequentially oriented lenses being comprised of:

-   -   at least two sequentially oriented elements, one of said at        least two sequentially oriented elements being of a shape and        orientation which individually converges a beam of        electromagnetic radiation caused to pass therethrough, and the        other being of a shape and orientation which individually        diverges a beam of electromagnetic radiation caused to pass        therethrough, there being a region between said first and second        elements such that, in use, a beam of electromagnetic radiation        sequentially passes through said first element, then said region        therebetween, and then said second element before emerging as a        focused beam of electromagnetic radiation; said lens system        being described by a selection, as shown in FIGS. 1 x-1 zz, from        the group consisting of:    -   1. a sequential combination of a converging element (C), a        diverging element (D), a converging element (C) and a diverging        element (D);        -   2. a sequential combination of a converging element (C), a            diverging (D) element, a diverging (D), element and a            converging (C) element;        -   3. a sequential combination of a diverging element (D), a            converging element (C), a diverging (D) element and a            converging (C) element;        -   4. a sequential combination of a diverging element (D), a            converging element (C), a converging element (C) and a            diverging (D) element.

And, of course, other sequential lens element configurations within thescope of the present invention include:

-   -   (Converging(C))(Converging(C))(Diverging(D));    -   (Diverging(D))(Diverging(D))(Converging(C));    -   (Converging(C))(Diverging(D))(Diverging(D));    -   (Diverging(D)) (Converging(C))(Diverging(D));    -   (Converging(C)(Converging(C))--(Diverging(D))(Diverging(D)); and    -   (Diverging(D))(Diverging(D))--(Converging(C))(Converging(C)).

Specific embodiments of a present invention lens system is furthercharacterized by at least one selection from the group consisting of:

-   -   a. the focal length of the lens system is between forty (40) and        forty-one (41) millimeters over a range of wavelengths of at        least two-hundred (200) to seven-hundred (700) nanometers; and    -   b. the focal length of the dual stage lens system varies by less        than five (5%) percent over a range of wavelengths of between        two-hundred and five-hundred nanometers; and    -   c. the spot diameter at the focal length of the lens system is        less than seventy-five (75) microns over a range of wavelengths        of at least two-hundred (200) to seven-hundred (700) nanometers.

At least one of said input and output lenses, when selected and present,can demonstrate properties selected from the group consisting of:

-   -   both demonstrating birefringence;    -   neither demonstrating birefringence;    -   one demonstrating birefringence and the other not.        Representative materials from which different elements in said        input and output lenses can be made made are calcium fluoride        (FE1) (FE1 a) (FE1 b), and fused silica (FE3), (FE3 a) (FE3 b).

FIG. 2 a shows an actual Focal Length vs. Wavelength plot for a multipleelement lens. FIG. 2 c demonstrates Spot Size as a function ofwavelength for said multiple element lens. FIG. 2 b is included to showthat where a cyclic variation exists in Focal Length vs. Wavelength, itis possible to identify at least two Wavelengths (λ2) and (λ3) where theFocal Lengths (λ2) are exactly equal. In some cases the Focal Lengths(λ1) will be exactly the same at three wavelengths (λ1), (λ4) and (λ5).Note that at (λ1) an (λ4) one focal length (λ1) exists, and at that at(λ2) and (λ3) a second focal length exists. This gives insight thatmoving a single lens toward or away from a sample can cause differentwavelengths to be selected at which the focal lengths are equal. Thusone embodiment of the invention allows for such lens motion as a meansfor enabling more than two wavelengths to investigate the same singlespot on a sample. This is indicated in FIG. 3 a 2.

Continuing, FIG. 3 a 1 demonstrates a simplified diagram showing anElectromagnetic beam (E) passing through a Converging Lens (F1),impinging on a Sample System (SS) and being recollimated by Lens (F2).FIG. 3 b demonstrates that a system can be constructed to allowpositioning a sequence of (S1), (S2) (S3) Systems which each containLens Systems (F1) (F2), (F1′) (F2′) and (F) (F2″), (with F2, F2′ and F2′being shown), into the pathway of the electromagnetic beam (E). A Guide(G) is shown along which the sequence of (S1), (S2) (S3) Systems canslide, which in FIG. 3 a 1 is into and out of the plane of the paper.

FIG. 3 a 2 indicates that a system can be constructed to allow moving alens (F1) toward or away from a sample, along the locus of theelectromagnetic radiation. Said lens motion can be applied to adjust thefocal length at a sequence of wavelengths and can enable achieving morethan two wavelengths which investigate the same spot on a sample. Thissystem allows Polychromatic electromagnetic radiation (E) from a sourcethereof to be focused onto said sample by said lens (F1) which ispositioned before said sample, and data obtained at wavelengths at whichfocal lengths are equal such that they are focused onto said sample atsubstantially exactly the same point thereupon. Then the lenses can bepositioned at a different distance from said sample, in a direction asshown, and again polychromatic electromagnetic radiation (E) from saidsource thereof will be focused onto said sample by said pre-sample lens(F1). Data at at least one wavelength at which the focal length of saidlens pre-sample lens (F1) is such as to be focused onto said sample atsubstantially exactly the same point thereupon as in step d can then beobtained. Only data obtained which corresponds to said substantiallysame point on said sample is used in sample analysis. Said data can beobtained using any number of wavelengths, as long as the correctwavelength(s) are selected at each position of the pre-sample lens (F1),with respect to said sample, so that the electromagnetic radiation isfocused onto the same spot thereon. Where the pre-sample (F1) lensprovides a plurality of wavelengths which have the same focal lengths ata position of said pre-sample lens (F1), with respect to said sample,then data can be simultaneously obtained thereat. However, as moving thepre-sample lens (F1) causes other wavelengths to provide focus on thesame spot on the sample, the configuration of FIG. 3 a 2 enablesobtaining data corresponding to the substnatially exactly the same spoton a sample at a great many number of wavelengths. It is noted that FIG.3 a 2 shows a lens (F2) after the sample, which serves to re-collimatefocused electromagnetic radiation which reflects from the sample.

FIG. 3 a 3 shows another approach to providing a sequence of lenses (F1)(F1′) (F1″) and (F2) (F2′) and (F2″) into the beam (E) ofelectromagnetic radiation. This system aloows a sequence of lenses,which are designed to provide the same focal lengths at differentwavelengths, can be moved into a beam of polychromatic electromagneticradiation (E).

It should be appreciated that by limiting data utilized to that achievedat and/or in an acceptable range around wavelengths at which the focallengths are substantially exactly the same in analysis, it is possbileto characterize a sample at a very precise point location thereupon.

Further, where two wavelengths are insufficient to adequatelycharacterize a sample at a single spot thereupon, it is possible toprovide a movable lens system, or multiple lens sets which each providethe same focal length at different wavelengths, but which wavelengthsare different from set to set.

It is to be understood that the term “Point” as utilized in thisSpecification is to be interpreted to mean that the areas a beam ofelectromagnetic radiation causes on a sample by two or more wavelengthstherein, are concentric about substantially the same location upon saidsample.

It is also to be understood that where a system of two lenses is referedto, it is means that one lens is prior to and another after a sample. Itdoes not mean or require that one or both of said two lenses can noteach be comprised of multiple lenses, or that one or both lenses can notbe of multiple element construction.

Further, where it is stated that a lens is placed at “a Focal Length”from a sample, said language is to be interpreted to include placementwithin practical deviations therearound.

Having hereby disclosed the subject matter of the present invention, itshould be obvious that many modifications, substitutions, and variationsof the present invention are possible in view of the teachings. It istherefore to be understood that the Invention may be practiced otherthan as specifically described, and should be limited in its breadth andscope only by the Claims.

Finally, FIGS. 4 a and 4 b are included to demonstrate that the presentinvention can be practiced in combination with evacuation or purging.FIG. 4 a shows a Chamber (CHA) to which are affixed Polarizartion StateGenerator (PSG) and Polarization State Detector (PSD). The path of thewavelengths therebetween, including interaction with a Sample (SS) canbe in an environment which does not attenuate wavelengths involved. FIG.4 b shows a purging system including a Source of ElectromagneticRadiation (LS) and a Polarizer (P), as well as an Analyzer (A) andDetector (DET) incombination with Cable means for relaying signals and aTube for entry of Purging Gas (GAS) near the Sample (SS).

Having hereby disclosed the subject matter of the present invention, itshould be obvious that many modifications, substitutions, and variationsof the present invention are possible in view of the teachings. It istherefore to be understood that the invention may be practiced otherthan as specifically described, and should be limited in its breadth andscope only by the Claims.

1. A method of analyzing substantially the exact same spot of a samplewith multiple wavelengths of electromagnetic radiation, comprises thesteps of: practicing steps a and b in either order, said steps a and bbeing: a) providing a selection from the group consisting of:ellipsometer; polarimeter; spectrophotometer; and reflectometer; whichsequentially comprises a source of polychromatic electromagneticradiation, a stage for supporting a sample and a detector; b) providinga lens system, comprising two lenses, which lens system has beendesigned to allow change of position of sid lenses with respect to asample, and which lenses optionally provide focal lengths which aresubstantially exactly the same at at least two specified wavelengths; c)placing one lens of said lens system provided in step b prior to asample which is positioned on said stage for supporting a sample, andanother thereof after said sample; d) causing polychromaticelectromagnetic radiation from said source thereof to become focusedonto said sample by said lens positioned before said sample, andobtaining data at at least one wavelength at which said electromagneticradiation is focused onto said sample at a point thereupon; e) movingthe lenses along the locus of the electromagnetic radiation to placethem at different distances from said sample and again causing saidpolychromatic electromagnetic radiation from said source thereof tobecome focused onto said sample by said lens positioned before saidsample, and obtaining data at at least one wavelength at which the focallength is such that the polychromatic electromagnetic radiation isfocused onto said sample at substantially exactly the same pointthereupon as in step d; f) utilizing only data obtained which correspondto said substantially same point on said sample in sample analysis.
 2. Amethod as in claim 1, wherein said lenses of the lens system comprise atleast two elements and which are designed to provide focal lengths whichare substantially exactly the same at two specified wavelengths.
 3. Amethod as in claim 2, wherein each of said at least two elements is madeof a material independently selected from the group consisting of: CaF₂;BaF₂; LiF; MgF₂; and fused silica; and wherein each of at least twoelements are individually selected to be made of different materials. 4.A method as in claim 1, wherein said lenses of said lens system providedin step b placed prior to a sample which is positioned on said stage forsupporting a sample, or thereafter, are characterized by a selectionfrom the group consisting of: both demonstrate birefringence; neitherdemonstrate birefringence; one demonstrates birefringence and the othernot.
 5. A method of analyzing a sample at the exact same spot with atleast two wavelengths of electromagnetic radiation, comprising the stepsof: practicing steps a and b in either order, said steps a and b being:a) providing a selection from the group consisting of: ellipsometer;polarimeter; spectrophotometer; and reflectometer; which sequentiallycomprises a source of polychromatic electromagnetic radiation, a stagefor supporting a sample and a detector; b) providing a lens system,comprising two lenses, which are designed to provide focal lengths whichare substantially exactly the same at two specified wavelengths; c)placing one lens provided in step b prior to a sample which ispositioned on said stage for supporting a sample, and one thereof aftersaid sample, each of said lenses being placed a focal length distancefrom a specific point on said sample; d. causing polychromaticelectromagnetic radiation from said source thereof to become focusedonto said sample by said pre-sample lens, such that two wavelengths arefocused onto said sample at substantially exactly the same pointthereupon; e) utilizing only data obtained at said wavelengths for whichthe focal lengths are substantially the same in sample analysis.
 6. Amethod of analyzing a sample at the exact same spot with at least twowavelengths of electromagnetic radiation as in claim 5, in which stepsa-d are repeated with said lenses placed at a different focal lengthdistances along the locus of the electromagnetic radiation from saidsample, so that focus is achieved at two wavelengths, at least one ofwhich is different from the two wavelengths in step b, and wherein stepe additionally utilizes data obtained at said additional different atleast one wavelength in said sample analysis.
 7. A method as in claim 5,wherein said lenses of said lens system comprise at least two elementsand which are designed to provide focal lengths which are substantiallyexactly the same at two specified wavelengths.
 8. A method as in claim7, wherein each of said at least two elements is made of a materialindependently selected from the group consisting of: CaF₂; BaF₂; LiF;MgF₂; and fused silica; and wherein each of at least two elements areindividually selected to be made of different materials.
 9. A method asin claim 5, wherein said lenses of said lens system provided in step bplaced prior to a sample which is positioned on said stage forsupporting a sample, or thereafter, are characterized by a selectionfrom the group consisting of: both demonstrate birefringence; neitherdemonstrate birefringence; one demonstrates birefringence and the othernot.
 10. A method of analyzing a sample at the exact same spot with atleast two wavelengths of electromagnetic radiation, comprising the stepsof: practicing steps a and b in either order, said steps a and b being:a) providing a selection from the group consisting of: ellipsometer;polarimeter; spectrophotometer; and reflectometer; which sequentiallycomprises a source of polychromatic electromagnetic radiation, a stagefor supporting a sample and a detector; b) providing a set of two lenseswhich have been designed to provide a first focal length which issubstantially exactly the same at first and second specifiedwavelengths, and a second focal length which is substantially exactlythe same at third and forth specified wavelengths; and c) placing one ofsaid lenses provided in step b prior to a sample which is positioned onsaid stage for supporting a sample, and one of said lenses provided instep b after said sample, each of said lenses being placed a focallength distance from a specific point on said sample; d) causingpolychromatic electromagnetic radiation from said source thereof tobecome focused onto said sample by said pre-sample lens, such that saidfirst and second wavelengths are focused onto said sample atsubstantially exactly the same point thereupon, such that via reflectionfrom said sample said two wavelengths are entered into said detector; e)causing said lenses to be moved toward or away from said sample alongthe locus of the electromagnetic radiation, such that the said third andforth wavelengths are focused onto said sample at substantially exactlythe same point thereupon as was investigated in step d, such that viareflection from said sample said two wavelengths are entered into saiddetector; f) causing polychromatic electromagnetic radiation from saidsource thereof to become focused onto said sample by said pre-samplelens, such that said two wavelengths are focused onto said sample atsubstantially exactly the same point thereupon, such that via reflectionfrom said sample said two wavelengths are entered into said detector; g)analyzing said sample utilizing only data provided by said detectorbased upon said first, second, third and forth wavelengths.
 11. Anellipsometer system sequentially comprising: a. a Source of apolychromatic beam electromagnetic radiation; b. a Polarizer element; c.optionally a compensator element; d. focusing means; e. a materialsystem; f. collimating means; g. optionally a compensator element; h. anAnalyzer element; and i. a Detector System; in which said focusing meansin d and collimating means in f comprise input and output lenses mountedto allow change of position thereof with respect to a sample, andoptionally provide focal lengths which are substantially exactly thesame at at least two specified wavelengths; such that in usepolychromatic electromagnetic radiation from said source thereof iscaused to become focused onto said sample and data is obtained atwavelengths at which focal lengths are equal such that they are focusedonto said sample at substantially exactly the same point thereupon;followed by moving the lenses along the locus of the electromagneticradiation to be at a different distances from said sample and againcausing said polychromatic electromagnetic radiation from said sourcethereof to become focused onto said sample by said pre-sample lens, andobtaining data at at least one wavelength at which the focal length issuch that the polychromatic electromagnetic radiation is focused ontosaid sample at substantially exactly the same point thereupon as in stepd; and utilizing only data obtained which correspond to saidsubstantially same point on said sample in sample analysis.
 12. A sampleanalysis system comprising: a) a source of beam of polychromaticelectromagnetic radiation; b) a scanning monochromater; c) a systemcomprising a lens and means for adjusting the position thereof in adirection along the locus of said beam; d) a sample; e) a systemcomprising a lens and means for adjusting the position thereof in adirection along the locus of said beam of polychromatic electromagneticradiation after it reflects from said sample; f) a detector; said systemfurther comprising a computer control system which is programmed toprovide signals to the scanning monochromater, the system comprising alens and means for adjusting the position thereof in a direction alongthe locus of said beam in c, and said a system comprising a lens andmeans for adjusting the position thereof in a direction along the locusof said beam of polychromatic electromagnetic radiation after itreflects from said sample in e; such that in use as the scanningmonochromater provides a sequence of wavelengths the the systemcomprising a lens and means for adjusting the position thereof in adirection along the locus of said beam in c, and said a systemcomprising a lens and means for adjusting the position thereof in adirection along the locus of said beam of polychromatic electromagneticradiation after it reflects from said sample in e move such that theirfocal lengths at each wavelength provided by said scanningmonochromater, the same substantially focused small spot is encounteredon said sample.
 13. A sample analysis system as in claim 12, whichfurther comprises a polarizer between said source of beam ofpolychromatic electromagnetic radiation and said sample, and an analyzerbetween said sample and said detector, and the system analysis system isan ellipsometer or polarimeter system.
 14. A sample analysis system asin claim 13, which further comprises at least one compensator situatedin the path of said beam of polychromatic electromagnetic radiationbetween said source of beam of polychromatic electromagnetic radiationand the detector thereof.
 15. A method as in claim 1 wherein resultsobtained by practice thereof are optical constants and are expressely oreffectively presented.
 16. A method as in claim 5 wherein resultsobtained by practice thereof are optical constants and are expressely oreffectively presented.
 17. A method as in claim 10 wherein resultsobtained by practice thereof are optical constants and are expressely oreffectively presented.
 18. A method as in claim 1 wherein evacuation ofpurging is practiced to reduce electromagnetic radiation intensityattentuation effects.
 19. A method as in claim 5 wherein evacuation ofpurging is practiced to reduce electromagnetic radiation intensityattentuation effects.
 20. A method as in claim 10 wherein evacuation ofpurging is practiced to reduce electromagnetic radiation intensityattentuation effects.